| 摘要 |
PROBLEM TO BE SOLVED: To enable the cryptoanalysis of both of a ciphertext sent to the entire part of a group and a ciphertext addressed to the receivers themselves to be performed with one secret key with each of the respective receivers by having the respective secret keys derived from the secret key of the group held by the respective receivers. SOLUTION: In the case of a cipher level 0, i.e., transmission to the entire part of the group, an integer n-0 to attain n-0=p-0*q-0 is determined with respect to arbitrary integers p-0 and q-0 (S1) and the Euler's function thereof is put as phi(n-0). And a-0*b-0=b-0=1 (mod phi(n-0)) is determined (S2) and the integers a-0 and b-0 are respectively determined as the public key and secret key of the cipher lever 0. In the case of the cipher level (i) to be sent only to the receiver (i), the integer n-i to attain n-i=p-i*q-i is determined with respect to arbitrary integers p-i and q-i (S6). The intrinsic integer is formed by using random numbers, etc., and this integer is determined as k-i. The secret key b-i of the receiver (i) is determined from b-i=b-0+k-i×phi(n-0) (S7).
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